CZTS stoichiometry effects on the band gap energy

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• 作者：Claudia Malerba ; Francesco Biccari ; Cristy Leonor Azanza Ricardo ; Matteo Valentini ; Rosa Chierchia ; Melanie M¨¹ller ; Antonino Santoni ; Emilia Esposito ; Pietro Mangiapane ; Paolo Scardi ; Alberto Mittiga
• 关键词：CZTS ; Kesterite ; Optical properties ; Band gap ; Defects ; Stoichiometry.
• 刊名：Journal of Alloys and Compounds
• 出版年：2014
• 出版时间：5 January, 2014
• 年：2014
• 卷：582
• 期：Complete
• 页码：528-534
• 全文大小：977 K

文摘

The considerable spread of Cu₂ZnSnS₄ (CZTS) optical properties reported in the literature is discussed in terms of material stoichiometry. To this purpose, kesterite thin films were prepared by sulfurization of multilayered precursors of ZnS, Cu and Sn, changing the relative amounts to obtain CZTS layers with different compositions. X-Ray Diffraction (XRD), Energy Dispersive X-Ray (EDX) spectroscopy, X-Ray Photoelectron Spectroscopy (XPS) and Raman spectroscopy were used for structural and compositional analysis. XRD quantitative phase analysis provides the amount of spurious phases and information on Sn-site occupancy. The optical properties were investigated by spectrophotometric and Photothermal Deflection Spectroscopy (PDS) measurements to assess the absorption coefficient of samples with different compositions. The PDS data show an increase of the sub-band absorption as the Sn content decreases. The results are interpreted assuming the formation of additional defects as the tin content is reduced. Those defects can also be responsible for the decrease of the band gap energy value as the Sn/Cu ratio is decreased.